The motivation of the present work is our research on a cantilever-based chemical sensor. We are addressing the question of the source of the surface stress on a gold-coated cantilever due to alkanethiol adsorption. By simultaneously measuring layer thickness and cantilever stress during alkanethiol monolayer self-assembly, the aim is to gain some insight on where the surface stress comes from. The technique we used to monitor layer thickness is ellipsometry. The ellipsometer is used to measure, in situ, the formation dynamics of self-assembled alkanethiol monolayers under different conditions. The thickness evolution is interpreted in terms of monolayer phases (lying-down and standing-up). During these experiments, the ellipsometer is proven to have Angstrom resolution. Following our objectives, a combined stress-thickness set-up is designed and built. Preliminary results are presented while further investigations are currently being made.

Magnetic quantum cellular automata (MQCA) have been proposed as an alternate computing architecture. Single domain magnetic particles represent "1" or "0"; their stray field interaction controls the propagation and manipulation of information. An inherent requirement for an MQCA system is to know the conditions under which nanomagnets switch between the purely "up" (1) and the purely "down" (0) state, and to control this reproducibly. / As a first step to study this, arrays of two types of permalloy particles were designed, simulated, fabricated and imaged, and their switching distributions ascertained. Individual particles were "peanut"-shaped, to investigate the effect of a shape anisotropy for an elliptical particle. Particles had long axes of 750 nm and 250 nm, but had identical aspect ratios. / Particles were simulated with a public domain software package, Object Oriented Micromagnetic Framework (OOMMF), fabricated by electron beam lithography with standard lift-off techniques in the fabrication facility in Sherbrooke, Canada, and imaged in vacuum using a custom built magnetic force microscope in constant height mode with an in plane, in-situ magnetic field. Ensemble hysteresis loops were obtained as was the average switching fields for both arrays. / The 750 nm particles were found experimentally to have a two-step switching process. The first switch occurred at 60 +/- 16 Oe and the second at 130 +/- 56 Oe. These results were nominally better than those obtained in a previous study on similarly sized ellipses. / Simulations on the 250 nm particles predicted that particles of that size would have the single domain configuration as their virgin state, and would have a one-step switching process. The switching field of a typical particle was calculated to be 550 +/- 30 Oe. This was confirmed experimentally, where the switching field distribution had its peak at 490 +/- 40 Oe. Thus, theory and experiment are in agreement, within error.

The epitaxial growth of ultrathin films of NaCl was achieved on a Cu(100) substrate at room temperature. The growth mode was observed to be of the Stranski-Krastanov type using non-contact AFM, with well-oriented square islands growing on top of the first monolayer of NaCl. The frictional properties of different monolayers were measured using contact mode AFM. The friction contrast between the different monolayers of NaCl was found to be too small to be measured within the noise. Atomic stick-slip measurements were performed on a NaCl island. The results are discussed in comparison with relevent literature on thin films of alkali halides.

The surface stress induced during the formation of alkanethiol [HS(CH 2)nCH3] self-assembled monolayers (SAMs) on gold from the vapor phase was measured using a differential cantilever-based sensor. This custom-built system is capable of surface stress measurements with a sensitivity of 5 x 10-5 N/m using commercially-available atomic force microscopy cantilevers. A second system combining cantilever-based sensing and ellipsometry was also designed and built, capable of yielding simultaneous in situ surface stress and film thickness measurements. Scanning tunneling microscopy (STM) with molecular resolution was also performed ex situ in order to characterize the structure of the resulting SAMs. The complementary use of these tools has provided an all-around view of the self-assembly process. / These measurements were performed in order to gain insight into the mechanisms involved in the self-assembly process and into the origins of the associated surface stress. Moreover, these studies were used to characterize and optimize the response of cantilever-based sensors based on functionalized SAM technology in terms of reliability, sensitivity, and reproducibility. / The evolution of the surface stress induced during alkanethiol SAM formation reveals features associated with coverage-dependent structural phase transitions. These results show that both the kinetics of SAM formation and the resulting SAM structure are strongly influenced by the surface structure of the underlying gold substrate, by the impingement rate of the alkanethiol molecules onto the gold surface, and by the cleanliness of the gold surface. In particular, it was found that a minimum gold grain size is necessary in order for the SAM to achieve the standing-up phase, for which large compressive surface stresses (~10 N/m) are measured. In addition, these results show that alkanethiol SAMs can become kinetically trapped in metastable intermediate states (lying-down phase) for formation on small-grained gold surfaces and/or at low alkanethiol vapor concentrations. Theoretical modeling of the origins of the induced surface stress reveals that inter-molecular Lennard-Jones interactions and electrostatic repulsion between adsorbed species play minimal roles in the development of the surface stress. Changes in the electronic structure of the underlying gold substrate are more likely to account for the large compressive surface stresses observed during alkanethiol SAM formation.

Electrochemically-induced changes in surface stress at the solid-liquid interface are measured using a differential cantilever-based sensor. The simultaneous, in situ measurements of the current (charge) and interfacial stress changes are performed by employing an AFM cantilever as both the working electrode (in a conventional three-probe electrochemical cell configuration) and as the mechanical transducer (bending of the cantilever). The custom-built instrument achieves a surface stress sensitivity of 1x10-4 N/m and a dynamic range of 5x105. Combining electrochemistry with cantilever-based sensing provides the extra surface characterization capability essential for the interpretation of the origin of the surface stress. / The objective of the present study is to gain a better understanding of the mechanisms responsible for the nanomechanical motion of cantilever sensors during adsorption and absorption processes. The study of these simple model systems will lead to a general understanding of the cantilever-based sensor's response and provide insights into the physical origin of the measured surface stress. / The surface stress generated by the electrochemically-controlled absorption of ions into a thin polypyrrole film is investigated. A compressive change in surface stress of about -2 N/m is measured when the polymer is electrochemically switched between its oxidized and neutral (swollen) state. The volume change of the polymer phase with respect to the gold-coated cantilever is shown to be responsible for the mechanical motion observed. / The potential-induced surface stress and surface energy change on an Au(111)-textured cantilever, in a 0.1 M HClO4 electrolyte, are simultaneously measured. These measurements revealed that for solid electrodes these two thermodynamic parameters are significantly different. In the double layer region, a surface stress change of -0.55 +/-0.06 N/m is measured during ClO4- adsorption whereas the surface energy variation is smaller by one order of magnitude. The origin of the surface stress change at the metal-electrolyte interface is understood by the variation in electron density at the surface which alters the inter-atomic bonds strength between surface atoms, while the specificity of adsorption of ions is found to be mostly responsible for the fine structure of the surface stress profile.

The electronic contribution to the resistivity rho and its temperature dependence were investigated for amorphous and crystalline [Fe xCo1--x] 33.3Zr66.7 (0 ≤ x ≤ 1) alloys in the temperature range 80--300 K. As Fe-rich compositions may exhibit spin fluctuation effects, transport properties were not studied below 80 K where spin fluctuation effects must be taken into consideration. The compositional and structural integrity of the samples was verified by means of X-ray diffractometry, electron-microprobe analysis, and differential scanning calorimetry. It was also confirmed that the first crystallization product for all the compositions is the face-centered cubic phase with the NiTi2-type structure. A true comparison between amorphous and crystalline transport properties was thus possible. For the metallic glasses, it was observed that rho( T) had a temperature dependence of the form: A + Bexp(--T/Delta) in agreement with Mizutani who proposed this relation for glasses containing a significant number of d-electrons at EF. The characteristic temperature, Delta, was found to be related to the Debye temperature, theta D, and the parameter B to the electronic specific heat coefficient, gamma. The resistivity data for the crystalline tenary compounds exhibited a (c -- bT + aT2)-dependence. Both the glasses and their crystalline counterparts were characterized by negative temperature coefficients of the resistivity, alpha. However, for the glasses, alpha increased as the Fe content increased whereas for the crystalline compounds alpha decreased as the Fe content increased.

The general theory of first principles calculations is presented and all equations are derived from basic starting points. In particular, an explanation of density functional theory (DFT) is given, with emphasis on the Hohenberg-Kohn theorem, the Kohn-Sham equations and the local density approximation (LDA). In addition, a description of pseudopotentials, basis sets, self-consistency, and solution methods for the Kohn-Sham equations will also be presented. Using these basics as a foundation, the equations needed to conduct an atomic orbital first principles calculation are then derived. This method incorporates the Harris approximation, LDA, a minimal sp3 atomic orbital basis set, and diagonalization to solve the Kohn-Sham equations. Finally, this technique is implemented and used to conduct calculations on small Si and Al clusters, bulk Si phase diagrams, Si band structures, Si(100) surface reconstruction, Al(111) surface relaxation, Si6 stability on the Si(100)2 x 1 surface, and Al nanowires.

We have used thermal conductivity measurements at low temperature to probe the behavior of the unconventional superconductor YBa2Cu 3O7-delta (YBCO). Two aspects were investigated: (1) the in-plane anisotropy, studied in order to gain insight into the contribution of CuO chains, and (2) the effect of a magnetic field, investigated in order to explore the contribution of vortices. Our results on the low temperature thermal conductivity are in good quantitative agreement with the theory for a d-wave superconductor. We have found a very weak (or even negligible) anisotropy suggesting that the anisotropy could not simply be explained by mass tensor anisotropy or the plasma frequency anisotropy. The magnetic field studies revealed an increase in the residual linear term (kappa/ T as T → 0) with field, reflecting the contribution to the density of states from the extended quasiparticles due to their Doppler shift in the presence of vortices. These results are in good quantitative agreement with the theoretical predictions.

The crossover transport regime between the quantum Hall effect and the Aharonov-Bohm effect is studied in terms of Buttiker's approach of electrical conduction. Quantum Hall effect and Aharonov-Bohm effect are very important effects in mesoscopic physics and both demonstrate unambiguously that quantum mechanics is the dominant factor in nanoscale electrical transport problems. However, they belong to situations of different dimensionality and different strength of magnetic fields. Our goal is to reveal the physics at the crossover regime between the two and find the transport properties of this transition regime. / We have computed Hall resistance of a four-probe box-shaped quantum dot with an artificial impurity confined inside. As the size of the impurity is increased, transport behavior changes from the usual quantum Hall regime to a regime dominated by strong Aharonov-Bohm (AB) oscillations. We observe directly the formation and coupling of the edge states and their effects on the Hall resistance, by varying a magnetic field. For a range of the impurity size, transport enters the crossover regime where quantum Hall and AB effects compete, and a peculiar approximate symmetry between various transmission coefficients lead to a Hall plateau before the quantum Hall regime is reached. This symmetry can be explained based on scattering matrix theory and a topological equivalence of the dominating transmission patterns where well defined edge states are formed. Finally we investigate the universality of the observed symmetry property in several other structures and find that within the scope of our calculation the symmetry is universal.

In this work we have re-examined the classical problem of nucleation and growth. We present a new model that combines steady-state homogeneous nucleation theory with the classical Lifshitz-Slyozov mechanism of growth. This model considers the substantial correlations between droplets and naturally incorporates the crossover from the early-stage, nucleation dominated regime to the scaling, late-stage, coarsening regime within a single framework, without ad-hoc assumptions. This is achieved by the development of a set of self-consistent interface equations which describe the decay of metastable states. The model is implemented numerically and some interesting dynamical behaviour is observed, including the reproduction of the expected late-time scaling and power-law growth laws for the key mean-field variables.